Various devices and methods have been used in the prior art for the fixation of bones or bone portions. In the case of procedures wherein the fixation of delicate bones is required, fine metallic wires are secured through holes drilled in the bones. Wires and pins of somewhat greater diameter can also be inserted through the bones with an apparatus such as a wire driver which resembles a rotary power drill. Staples have been employed as well to fixate osteotomy sites. In the case of larger bones, particularly in the reduction of fractures, self-tapping bone screws are often inserted into drill holes to secure portions of the bone on either side of the fracture and enable healing to occur.
Where greater stabilization is required or where in the case of a fracture, for example, a substantial amount of stress will be placed on the fragmented bone portions because of the position of the fracture, the weight of the patient, the nature of athletic or other activity in which the patient wishes to engage, or similar factors, bone-fixating compression plates are often placed across the fracture line and are anchored by screws inserted through the plates and into the bone on either side of the fracture.
In the open reduction and minimally invasive internal fixation of a variety of fractures of the proximal femur and femoral neck, combination screw and plate devices have been utilized wherein a cavity in the femoral neck is reamed out and a plate is put against the outer surface of bone through which a large screw or bolt is inserted and screwed into the reamed-out cavity. The screw or bolt is attached to a plate which abuts against the cortex of the femur. The plate is anchored in the bone by smaller bone screws.
The use of prior art devices such as screws or screw and plate combinations where compression of bone portions, for example in the case of fractures, is required, has significant drawbacks. Bone screws are normally inserted through the cortex of a bone and secured in the relatively soft bony material in the medulla, and the primary compressing force is provided by threads of the screw gripping into the medulla and the head of the screw pressing against the cortex. Particularly in the case of osteoporotic bone, the bone screws frequently do not provide sufficient compression on the bone to reduce the fracture properly.
In addition, when bone screws are used, even in cases where the opposite cortex is purchased, a very large hole is created through the cortex and medullary bone which cannot be filled in with bony material while the screw is in position. If the screw is removed, the areas of the bone immediately surrounding the screw hole have a greater susceptibility to cracking or fracturing than normal bone, and the bone is not filled in by natural healing processes for a considerable amount of time.
An example of a prior art device 100 is shown in FIG. 1. The prior art device 100 includes a nail-hip screw system whereby a nail 102 is inserted down the femur shaft. One or two gliding screws 104a, 104b are inserted into the femoral neck at 130°. Thus, the gliding screws 104a, 104b are positioned in parallel to each other and do not engage with each other.
Another example of a prior art device 40 is shown in FIG. 2. The prior art device 40 includes a bone plate 42 secured to the bone 44 by screws 46a to 46f, which are inserted through holes in bone plate 42 and into the bone about fracture 47 to hold the fragments of bone 44 in place until bone 44 heals. Bone plate 42 is shown as a blade plate, including plate portion 48 having a plurality of holes there through for receipt of screws 46a to 46f, and blade portion 50 extending from plate portion 48 to define an angle there between. Plate portion 48 and blade portion 50 are connected at bend 52, which defines fillet radius intermediate plate portion 48 and blade portion 50. It may be seen that, due to the large size of fillet radius (non conformal shape of the bone), a large gap 56 exists between plate portion 48 and outer surface 58 of bone 44 adjacent bend 52, wherein bend 52 projects outwardly of outer surface 58 of bone 44. Screws 46a to 46f include strut screw 46c, which is disposed through one of the holes in plate portion 48 and extends towards blade portion 50 of blade plate 42 such that end 60 of strut screw 46c abuts blade portion.
It is an object of the present invention to provide a surgical implant device having screws that can cater for combined loading (axial, bending and tension) and mimic nature's way of load transfer via the trabecular pattern of bone.
It is another object of the present invention to reduce the implant material thus becoming “Mini-Max” implant, due to the locking nature of the screws and the load being shared among all parts of the implant.
It is yet another object of the present invention to reduce the “Z-type” failures sometimes seen in other intramedullary implants. This unique type of failure results from differential fixation stability of two diameters of parallel screws into a femoral neck subject to oscillating motion during the recovery period.
Other objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.